These are all sources. Some individuals feel queezy over the thought of used bars given much that's been written of failures. I haven't had them fail but then again the last time I said that a half dozen members posted that they had. This was last week. Stems were the source of the problem, a particular type but still the two are related. So much for that.
If you're going to bother to put the bars on; with the lever, taping.. WHY NOT reach for a set of wider ones, it makes alot of difference. Chances are that donor bikes are cheaper and or older. Older bikes, even as late as the late '80s had 38 to at MOST 40cm bars. I've e-bay and ended up with "used" bars, 44cm & others that had never seen a stem or tape. Virtually brand new. Niag. NB, others seem fine.

Again, if you're investing the time, why not IMPROVE over that which was.
If you wear a size 38" jacket, weigh 135.. OK, stay with a 38cm. If you're an avg. size 21st cent. Amerian male, 38 (for many 40 ) is just plain dinky.